The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In oilfield operations such as sand control, it is generally desirable to constantly monitor the density of an oilfield fluid (such as proppant slurries) being pumped into the well. One approach to achieve this is to use a contact-based densitometer to directly measure the oilfield fluid being passed through a pipe or a container. The flow rate of the oilfield fluid is measured and the density of the oilfield fluid is then calculated. Equipment in this category includes, but is not limited to, mass flowmeters, hydrometers, etc. However, because the equipment is directly exposed to the oilfield fluid being measured, it is often susceptible for failure during oilfield operations due to the highly corrosive or highly abrasive nature of oilfield fluids.
Another approach is by using a non-contact densitometer to indirectly measure the oilfield fluid in a pipe or a container during an oilfield operation. The most widely used equipment in this category is the radioactive densitometer. It typically comprises a radiation source (such as radioactive cesium or cobalt) and a radiation detector. The radiation source is positioned on one side of a pipe or container and the radiation detector is positioned on the other side of the pipe or container. The radiation source emits radiation waves (such as gamma rays) and the radiation detector measures the attenuation of the radiation waves after they pass through the oilfield fluid. A processor then calculates the density of the oilfield fluid based on the signal detected. During the entire procedure, the radioactive densitometer does not contact the oilfield fluid being measured, hence the name “non-contact” densitometer.
One major disadvantage associated with using radioactive densitometers is the stringent regulations imposed by the government of various jurisdictions on the proper handling, transportation and storage of radioactive materials used in the radioactive densitometer. Accordingly, efforts have been made to use non-radioactive system to measure the density of oilfield fluids. For example, in one article, a Coriolis mass flowmeter was used to measure fluid densities. SPE23262, “Nonradioactive Densitometer for Continous Monitoring of Cement Mixing Process” (1991). However, the measuring tube in the Coriolis mass flowmeter can be eroded very quickly when the abrasive proppant slurries are pumped at a high rate through the flowmeter. Moreover, when the oilfield operation is to be conducted at high rates (such as 30 BPM) and/or involving tubes with big diameters (such as 6 inches or higher), the Coriolis mass flowmeter quickly becomes large in size and highly expensive.
US Patent Application Publication No. 2008/0115577 discloses a method of manufacturing a high pressure vibrating tube densitometer comprising enclosing twin flow tubes within an outer shell where the outer shell comprises portals for the installation or replacement of internal components. US Patent Application Publication No. 2004/0007059 discloses a method of determining the concentration of a particulate added to a fluid stream comprising the steps of measuring the rate of flow of the fluid stream, determining the rate of particulate flow by using an acoustic sensor and then calculating the concentration of the particulate in the fluid stream using results from the measuring and determining steps.
There remains a need for a non-contact, non-radioactive densitometer that solves one or more of the above identified problems.